1. Field of the Invention
The present invention relates to a control apparatus for starting a direct current (DC) brushless motor and a method thereof. More specifically, the present invention relates to a control apparatus for starting a DC brushless motor without a sensor and a method thereof.
2. Descriptions of the Related Art
In detecting the correct position of a rotor in a DC brushless motor during the start-up period, the conventional practice is to place a sensor (e.g., a Hall sensor) within the motor. The sensor is configured to sense the variation of the magnetic field between the rotor and the sensor when the motor is running to obtain information about the rotor position. However, the Hall sensor needs to be placed into the motor module with a precise position, which makes it difficult during assembly and increases production costs in small motors.
In an attempt to decrease the assembly difficulties and the production costs of small motors, DC brushless motors have been developed without sensors and have been used in various products that require drives. Generally, for most motors, the speed thereof can be well controlled when running at a medium or high rotational speed. However, in a stationary state, it is difficult to detect the rotor position. As a result, a particular starting procedure must be implemented to ensure that the motor can be started up in the normal driving mode.
Many conventional technologies used to start a DC brushless motor without a sensor have already been proposed, such as U.S. Pat. No. 5,343,127 and U.S. Pat. No. 7,202,623. According to both U.S. patents, a back electromotive force (BEMF) generated across the rotor winding in response to the rotational movement thereof is detected as the reference for determining the rotor position to start the motor. Unfortunately, these technologies require complex operations to start the motor, causing increased difficulties in controlling the motor.
Accordingly, it is highly desirable in the art to provide a control method and a circuit thereof that eliminates the need of a sensor and complex operational procedures while still appropriately starting a DC brushless motor.